gnutls-cli
TLS/SSL connection testing and debugging client
TLDR
Connect to TLS server
$ gnutls-cli [example.com]
Connect on specific port$ gnutls-cli -p [443] [example.com]
Show certificate chain$ gnutls-cli --print-cert [example.com]
Test with specific protocol$ gnutls-cli --priority="NORMAL:-VERS-TLS-ALL:+VERS-TLS1.3" [example.com]
Start with STARTTLS$ gnutls-cli --starttls-proto=[smtp] [mail.example.com]:587
Verify certificate only$ gnutls-cli --tofu [example.com] < /dev/null
SYNOPSIS
gnutls-cli [options] hostname
DESCRIPTION
gnutls-cli is a TLS/SSL client for testing and debugging secure connections. It connects to servers, displays certificate information, and allows testing of various TLS configurations.The tool helps diagnose certificate issues, protocol support, and cipher suite negotiation. It can also serve as a simple secure client for interactive protocols.
PARAMETERS
-p, --port port
Connect to port.-s, --starttls
Establish a plain-text session first and switch to TLS on EOF or SIGALRM (generic STARTTLS).--print-cert
Print server certificate.--starttls-proto proto
Use STARTTLS (smtp, pop3, imap, ftp, xmpp, ldap).--priority string
Priority string for cipher selection.-V, --verbose
Verbose output.--tofu
Trust on first use.--insecure
Don't verify certificate.-x, --x509cafile file
CA certificate file.--benchmark-ciphers
Benchmark cipher performance.--list
List supported algorithms.-d, --debug LEVEL
Set debugging verbosity level.
INSTALL
sudo apt install gnutls-bin
sudo dnf install gnutls-utils
sudo apk add gnutls-utils
CAVEATS
Certificate verification requires proper CA setup. Priority string syntax complex. Some servers may behave differently with test clients.
HISTORY
gnutls-cli is part of GnuTLS, developed by Nikos Mavrogiannopoulos and others starting in 2000. GnuTLS provides an alternative to OpenSSL under the LGPL license, and gnutls-cli serves as its diagnostic and testing tool.
